How can I change a sphere's radius with a Python script?
There are many ways to do this, the least complicated approach is probably this:

import bpy

properties = [
   [[-2, 0, 0], 0.2],
   [[-1, 0, 0], 0.3],
   [[+0, 0, 0], 0.4],
   [[+1, 0, 0], 0.5],
   [[+2, 0, 0], 0.6]
]

# [co]ordinate, and [r]adius 
for co, r in properties:
    bpy.ops.mesh.primitive_uv_sphere_add(segments=34, size=r, location=co)




See the documentation for UV Sphere

Depending on scene complexity other approaches will make more sense.